In a process of manufacturing a semiconductor device, a chemical mechanical polishing (CMP) technique can be used for planarizing an insulating film, a metal film, and/or a polycrystalline silicon film which are embedded in a groove. In the CMP, the surface of a polishing pad is deformed as the polishing is repeatedly performed, and a polishing performance is degraded. Therefore, the polishing pad is dressed by using a dresser for a certain time interval to suppress the degradation.